Stereological analysis of mitochondria from brains of temperature acclimated goldfish, Carassius auratus L. (5 and 30°C)

1. 1.|The mitochondrial population in hypothalamic and hypophysial brain tissue from warm (30°C) and cold (5°C) acclimated goldfish (Carassius auralus L.) was analyzed using sterological techniques.

2. 2.|It was revealed that there is a significantly larger volume density (Vv) in the cold acclimated tissue, with no significant difference in either of the surface densities (Svext and Svint) from either of the brain areas.

3. 3.|The hypothalamic brain tissue has a significantly lower specific surface (S/V) in the cold acclimated tissue but there is not a significant difference in this parameter for the hypophysial brain tissue.

4. 4.|The values for these three parameters (Vv, Svext and SVint, and S/V) indicate that mitochondria from acclimated brain tissue undergo shape changes in response to thermal stress.

5. 5.|We suggest that the shape changes may be related to the change in the phospholipid composition of the inner mitochondrial membrane with acclimation temperature.

Changes in parameters of the plasmalemma ATPase during cold acclimation of apple (Mains domestica) tree bark tissues

A plasmalemma fraction was isolated from homogenized apple tree (Mains domestica Borkh 'Golden Delicious') hark tissues using aqueous phase partitioning and ultra-centrifugation. Results of marker enzyme assays indicated that a membrane preparation highly enriched in plasma membranes was obtained. ATPase activity in this preparation possessed a high specificity for ATP as substrate, was inhibited by vanadate, diethylstilbcsterol and dicyclohexylcarbocHimide, and was insensitive to inhibitors of mitochondria! and tonoplasl ATPases. Specific activity of the plasma-lemma ATPase increased during cold acclimation prior to the attainment of vegetative maturity. Kinetic parameters (Km, Vln) determined from assays performed at different temperatures (10, 30°C) indicated a differential effect of cold acclimation on enzyme activity. Vm increased during cold acclimation, whereas Km increased when determined at 30°C but declined at 10°C. Acclimation treatments during April and May resulted in alteration of ATPase kinetics in the absence of any increase in bark frost hardiness. Changes in ATPase kinetics may be related more to enhanced low temperature metabolism than to frost hardiness per se.     

Abscisic acid deficiency prevents development of freezing tolerance in Arabidopsis thaliana (L.) Heynh.

Summary Abscisic acid (ABA) has been implicated as a regulatory factor in plant cold acclimation. In the present work, the cold-acclimation properties of an ABA-deficient mutant (aba) of Arabidopsis thaliana (L.) Heynh. were analyzed. The mutant had apparently lost its capability to cold acclimate: the freezing tolerance of the mutant was not increased by low temperature treatment but stayed at the level of the nonacclimated wild type. The mutational defect could be complemented by the addition of exogenous ABA to the growth medium, restoring freezing tolerance close to the wild-type level. This suggests that ABA might have a central regulatory function in the development of freezing tolerance in plants. Cold acclimation has been previously correlated to the induction of a specific set of proteins that have been suggested to have a role in freezing tolerance. However, these proteins were also induced in the aba mutant by low temperature treatment.     

The influence of high levels of brief or prolonged supplementary far-red illumination during growth on the photosynthetic characteristics, composition and morphology of Pisum sativum chloroplasts

Abstract. Peas were grown in controlled environments (12h white fluorescent light. ∼47 μmol photons m^-2 s 1/12 dark, 25 °C), using (1) 15-min far-red illumination at the end of each photoperiod (brief FR) to simulate the increase in the far-red/red ratio near the end of the day, and (2) high levels of supplementary far-red light (red:far-red ratio=0.04) during the entire photoperiod (long-term FR) to simulate extreme shade conditions under a plant canopy. Brief FR illumination led to marked morphological effects attributable to phytochrome regulation, namely, an increase in internodal length, but a decrease in leaflet area, chloroplast size and chlorophyll content per chloroplast compared with the control. Significantly, brief FR illumination had little or no effect on the amounts of the major chloroplast components (ribulose 1.5-biphosphate carboxylase, adenosine triphosphate synthase, cytochrome b/f complex and Photosystem II) relative to chlorophyll or Photosystem I, and the leaf photosynthetic capacities per unit chlorophyll were similar. In contrast, supplementing high levels of far-red light during the entire photoperiod not only led to the phytochrome effects above, but there was also a marked increase in leaf photosynthetic capacity per unit chlorophyll. due to increased amounts of the major chloroplast components relative to chlorophyll or Photosystem I. We hypothesize that supplementary far-red light, absorbed by Photosystem I, induced an increase in the major chloroplast components by a photosynthetic feedback mechanism. In fully greened leaves, we propose that the two photosystems themselves, rather than phytochrome, may be the predominent sensors of light quantity in triggering modulations of the stoichiometries of chloroplast components, which in turn lead to varying photosynthetic capacities.     

Three-dimensional finite element stress analysis of the dentate human mandible.

The biomechanical events which accompany functional loading of the human mandible are not fully understood. The techniques normally used to record them are highly invasive. Computer modelling offers a promising alternative approach in this regard, with the additional ability to predict regional stresses and strains in inaccessible locations. In this study, we built two three-dimensional finite element (FE) models of a human mandible reconstructed from tomographs of a dry dentate jaw. The first model was used for a complete mechanical characterization of physical events. It also provided comparative data for the second model, which had an increased vertical corpus depth. In both cases, boundary conditions included rigid restraints at the first right molar and endosteal cortical surfaces of the articular eminences of temporal bones. Groups of parallel multiple vectors simulated individual masticatory muscle loads. The models were solved for displacements, stresses, strains, and forces. The simulated muscle loads in the first model deformed the mandible helically upward and toward its right (working) side. The highest principal stresses occurred at the bite point, anterior aspects of the coronoid processes, symphyseal region, and right and left sides of the mandibular corpus. In general, the observed principal stresses and strains were highest on the periosteal cortical surface and alveolar bone. At the symphyseal region, maximum principal stresses and strains were highest on the lower lingual mandibular aspect, whereas minimum principal stresses and strains were highest on its upper labial side. Subcondylar principal strains and condylar forces were higher on the left (balancing or nonbiting) side than on the right mandibular side, with condylar forces more concentrated on the anteromedial aspect of the working-side condyle and on the central and lateral aspects of the left. When compared with in vivo strain data from macaques during comparable biting events, the predictive strain values from the first model were qualitatively similar. In the second model, the reduced tensile stress on the working-side, and decreased shear stress bilaterally, confirmed that lower stresses occurred on the lower mandibular border with increased jaw depth. Our results suggested that although the mandible behaved in a beam-like manner, its corpus acted more like a combination of open and closed cross sections due to the presence of tooth sockets, at least for the task modelled.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pyridine Nucleotide Changes In Hepatocytes Exposed To Quinones

Quinones may be toxic by a number of mechanisms. including arylation and oxidative stress caused by redox cycling. Using isolated hepatocytes, we have studied the cytotoxicity of four quinones. with differing abilities to arylate cellular nucleophiles and redox cycle. in relation to their effects on cellular pyridine nucleotides. High concentrations of menadione (redox cycles and arylates). 2-hydroxy-1,4-naphthoquinone (neither arylates nor redox cycles via a one electron reduction) 2.3-dimethoxy-1.4-naphthoquinone (a pure redox cycler) and p-benzoquinone (a pure arylator) caused an initial decrease in NAD⁺ and loss of viability, which was not prevented by 3-aminobenzamide. an inhibitor of poly(ADP-ribose)polymerase. In contrast. 3-aminobenzamide inhibited the loss of NAD' and viability caused by dimethyl sulphate so implicating poly(ADP-ribose)polymerase in its toxicity but not that of the quinones. Non-toxic concentrations of menadione. 2.3-dimethoxy-1.4-naphthoquinone and 2-hydroxy-1.4-naphthoquinone all caused markedly similar changes in cellular pyridine nucleotides. An initial decrease in NAD⁺ was accompanied by a small. transient increase in NADP⁺ and followed by a larger. prolonged increase in NADPH and total NADP⁺ + NADPH. Nucleotide changes were not observed with non-toxic concentrations of p-benzoquinone. Our findings suggest that a primary event in the response of the cell to redox cycling quinones is to bring about an interconversion of pyridine nucleotides. in an attempt to combat the effects of oxidative stress     

Effect of temperature on the optimal substrate for β-oxidation

The enzyme carnitine palmitoyl tranferase (CPT) is able to use a range of fatty acids as substrates, with some variation in catalytic rate among tissue. The substrate giving maximal activity of the enzyme under optimal conditions (C16: 1) is similar in trout, salmon, goldfish, eel and tilapia. There is no evidence that thermal acclimation affects substrate preference for β-oxidation.     

Cellular Stress Causes Accumulation of the Glucose Transporter at the Surface of Cells Independently of their Insulin Sensitivity

The stimulation of glucose transport in response to various types of stress has been studied. There is no relationship between effects of stress-inducing agents on glucose transport and their effects on cellular protein synthesis. Although the effect of stress on glucose transport appears analogous to its stimulation by insulin, cells that are slightly insulin-sensitive in terms of glucose transport (BHK cells) show a similar degree of stimulation as highly insulin-sensitive cells (differentiated 3T3-L1 cells). External labeling of the transporter protein with a photoactivatable derivative of mannose, 2-N-4-(1-azi-2,2,2-trifluoroethyl) benzoyl-1, 3-bis-(D-mannos-4-yloxy)-propylamine, shows that most of the increased glucose transport activity correlates with an increase in the amount of the transporter on the cell surface. Cells subjected to K⁺-depletion, which inhibits endocytosis and results in an accumulation of receptors at the cell surface, show the same increase in glucose transport as cells exposed to stress; stressed cells show no further increase in glucose transport when subjected to K⁺ depletion. These results support the view (Widnell, C.C., Baldwin, S.A., Davies, A., Martin, S., Pasternak, C.A. 1990. FASEB J 4:1634–1637) that cellular stress increases glucose transport by promoting the accumulation of glucose transporter molecules at the cell surface. Received: 20 June 1995/Revised: 29 September 1995     

Seasonal patterns of dehydrins and 70-kDa heat-shock proteins in bark tissues of eight species of woody plants

Although considerable effort has been directed at identifying and understanding the function and regulation of stress-induced proteins in herbaceous plants, reports concerning woody plants are limited. Studies with herbaceous crops have revealed similarities in the types of proteins that accumulate in response to a wide array of abiotic stresses and hormonal cues such as the accumulation of abscisic acid. Many of the identified proteins appear to be related to dehydrins (the D-11 subgroup of late-embryogenesis-abundant proteins). The objective of the present study was to determine if seasonal induction of dehydrins is a common feature in woody plants and to see if seasonal patterns existed for other stress-induced proteins. Bark tissues from eight species of woody plants were collected monthly for a period of 1.5 years. The species included: peach (Prunus persica) cv. Loring; apple (Malus domestica) cv. Golden Delicious; thornless blackberry (Rubus sp.) cv. Chester; hybrid poplar (Populus nigra); weeping willow (Salix babylonica); flowering dogwood (Cornus florida); sassafras (Sassafras albidum); and black locust (Robinia pseudo-acacia). Immunoblots of bark proteins were probed with a polyclonal antibody recognizing a conserved region of dehydrin proteins, and monoclonal antibodies directed against members of the HS70 family of heat-shock proteins. Some proteins, immunologically related to dehydrins, appeared to be constitutive; however, distinct seasonal patterns associated with winter acclimation were also observed in all species. The molecular masses of these proteins varied widely, although similarities were observed in related species (willow and poplar). Identification of proteins using the monoclonal antibodies (HSP70, HSC70, BiP) was more definitive because of their inherent specificity, but seasonal patterns were more variable among the eight species examined. This study represents only a precursory examination of several proteins reported to be stress related in herbaceous plants, but the results indicate that these proteins are also common to woody plants and that further research to characterize their regulation and function in relation to stress adaptation and the perennial life cycle of woody plants is warranted.